Paul Ceglia, the man who claims he has a contract that entitles him to 50 percent ownership in Facebook, has lost his high-power legal representation at a critical juncture in the case.

Ceglia filed a notice of substitution of counsel today with the U.S. District Court for the Western District of New York to replace the law firm of DLA Piper, a 4,200-attorney international law firm, with the San Diego-based Lake law firm, a firm of four lawyers that also represents 200 medical marijuana collectives.

DLA Piper's withdrawal comes on the day that Ceglia's latest filing was due and ahead of Thursday's scheduled hearing on expedited discovery.

A DLA Piper spokesman confirmed the law firm had withdrawn from the case but declined to comment further.

"We have withdrawn from the case and no longer represent Paul Ceglia," said DLA Piper spokesman Brian Kiefer. "Due to our attorney-client privilege obligations, there will be no further comment."

Facebook declined to comment on the filing and representatives for Lake did not immediately respond to a request for comment.

This is the third time Ceglia has changed legal representation in the case. Former New York attorney general Dennis Vacco and Terrence Connors have also represented Ceglia in the matter.

DLA Piper began representing Ceglia in April when he filed a revised complaint against Facebook and its chief executive and co-founder, Mark Zuckerberg. In the filing, Ceglia cited more than a dozen e-mails purportedly between himself and Zuckerberg that detail discussions on design, development, business plans, and eventual contract disputes regarding The Face Book, as it was then called.

In a filing responding to Ceglia's revised lawsuit, Facebook and Zuckerberg called the e-mails forgeries. "The contract is a cut-and-paste job, the e-mails are complete fabrications, and this entire lawsuit is a fraud," Facebook said and requested it have the opportunity to inspect the original contract, e-mails in native form, and all computers in Ceglia's possession as well as those in his parents' house.

DLA Piper said in a statement at the time that "Mr. Ceglia welcomes the opportunity to expedite discovery in this case."

Ceglia, of Wellsville, N.Y., claimed in a lawsuit filed last year that he entered into a contract with Zuckerberg in 2003 to design and develop the Web site that would ultimately become Facebook--a company that now has an estimated value of more than $70 billion.

Ceglia said he hired Zuckerberg through a Craigslist ad to write code for a project called StreetFax and paid Zuckerberg $1,000 for coding work; he also allegedly invested $1,000 in Zuckerberg's The Face Book project, which gave him a 50 percent interest in the company as well as an additional 1 percent interest for every day after January 1, 2004, that The Face Book was delayed.

Zuckerberg acknowledged that he signed a contract to write code for StreetFax but said the contract was "doctored" to make it appear to be about Facebook development.

Last year, Ceglia produced a canceled check that he said proved he paid Zuckerberg $3,000 for some freelance software development work for a project called "The Face Book." Facebook initially said it believed the contract was a "likely" forgery. It has since become more forceful and said it considers it to be an outright fake.